SPC MD 1780


MD 1780 Image

Mesoscale Discussion 1780
NWS Storm Prediction Center Norman OK
0128 PM CST Tue Nov 10 2020

Areas affected...northern IL and including the greater Chicago
metro...southeast WI

Concerning...Severe potential...Tornado Watch likely 

Valid 101928Z - 102100Z

Probability of Watch Issuance...80 percent

SUMMARY...A tornado watch is likely by 3pm CST for northeast IL
northward into southeast WI.  The forecast primary severe hazards
are 55-70 mph gusts and a QLCS mesovortex threat capable of
brief/weak tornadoes and/or narrow swaths of stronger gusts.  The
supercell tornado threat is conditional and a bit more uncertain. 
The greatest tornado risk will generally be located north of I-80 to
the east/southeast of the surface low.

DISCUSSION...The radar mosaic as of 125pm CST shows a squall line
from the IA/MO/IL border extending southward into central MO.  A
stalled surface front largely parallels the IA/IL border extending
northeast into southeast WI.  Surface temperatures have warmed into
the lower 70s F with dewpoints around 60 F in the warm sector
south/east of the boundary.  The 1pm Lincoln, IL special raob showed
a 10.4 lowest 100 mb mean mixing ratio suggesting limited additional
increase in low-level moisture is not likely (i.e., dewpoints rising
into the 62-64 deg range).  Likewise, the 19z Davenport, IA special
raob showed a similar boundary layer moisture profile---lending
confidence in this moisture assessment.  

Both special raobs showed enlarging hodographs and this is occurring
in observed data at the KMKX and KLOT VADs.  RAP forecast soundings
for 4pm-7pm across northeast IL and southeast WI show larger CAPE
(due to the aggressive low-level moisture scenario) than what will
probably occur.  Given the overall weak CAPE/high shear setup in a
strongly forced regime, it appears a squall line with an attendant
damaging wind/severe gust hazard will be the primary risk, along
with the possibility for a few weak/brief QLCS mesovortex tornadoes.
The main corridor for severe will probably focus across northern IL
into southeast WI to the east/southeast of the surface low track
this afternoon/evening.

..Smith/Hart.. 11/10/2020

...Please see www.spc.noaa.gov for graphic product...


LAT...LON   42468993 43418895 43788775 43438754 41878731 40578793
            40598859 41518940 42468993 

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